In certain types of surgery, a cannula is used to provide a passageway into a body cavity through which surgical instruments may be passed. Cannulas are typically elongate rod-like members having a bore therethrough the surgical instrument may be passed through the bore. At times, the body cavity will be insufflated by a gas and at all times, the cannula will be subjected to internal body fluids. Therefore, some form of seal assembly is necessary to allow the surgical instrument to pass while maintaining sealed integrity around the instrument such that the insufflation gas, the internal body fluids, or both, cannot escape.
Typically, in conventional devices, such a seal mechanism will include a housing for mounting on the cannula, with the housing having a bore therethrough for passage of the surgical instrument. Two seals are typically located within the housing. The lower housing contains a seal, typically called a duckbill valve that assists maintaining gases and fluids in place when an instrument is not inserted within the duckbill valve. The duckbill valve is typically formed from flexible material and includes a slit opening that gives way to the instrument upon insertion. The upper housing typically includes a valve seal that includes a relative wide access opening and a relatively narrow valve opening. The valve opening can expand to accommodate the surgical instrument and is sufficiently resilient to form a seal around the instrument upon insertion.